Molecular subtype-driven disparities in intraoperative touch imprint cytology accuracy for sentinel lymph node assessment in clinically node-positive breast cancer treated with neoadjuvant chemotherapy.

BACKGROUND: This study aimed to investigate the impact of molecular subtype on the accuracy of intraoperative touch imprint cytology (ITPC) for sentinel lymph node (SLN) evaluation in clinically axillary node-positive (cN +) breast cancer patients treated with neoadjuvant chemotherapy (NAC). METHODS: We conducted a retrospective cohort study of 232 cN + breast cancer patients undergoing NAC followed by SLN biopsy with ITPC. Diagnostic performance values (sensitivity, specificity, NPV, false-negative rate, etc.) were calculated against final histopathological diagnosis, and stratified by molecular subtypes. RESULTS: ITPC identified 53 positive cases (23 false-negatives) across 917 SLNs, demonstrating 69.74% sensitivity, 100% specificity, and 87.15% NPV. HER2-positive (nonluminal) tumors showed the highest tpCR (67.53%) with a moderate SLN-positive rate (24.14%) and the lowest false-negative rate (3.90%). Luminal B (HER2-positive) tumors exhibited a moderate tpCR (57.89%) and a SLN-positive rate (29.31%) but a higher false-negative rate (13.79%). In contrast, both Luminal A and Luminal B HER2-negative displayed lower tpCRs (0.00% and 20.00%), higher SLN-positive rates (66.67% and 57.78%), and higher false-negative rates (33.33% and 22.22%). Notably, TNBC showed a tpCR of 48.98%, a SLN-positive rate of 34.69%, and the lowest false-negative rate of 2.04%. Chemotherapy-induced changes in SLNs (OR = 11.155, 95% CI 2.002-62.152; p = 0.006) and residual micrometastases/ITCs (OR = 37.843, 95% CI 5.031-284.671; p < 0.0001) were independent influencing factors of false-negative results. CONCLUSIONS: Collectively, our study demonstrates that ITPC exhibits a robust accuracy for detecting SLN metastases in cN + breast cancer patients treated with NAC. The findings support the implementation of molecular subtype-specific SLN management: ITPC alone may be adequate for HER2-positive and TNBC tumors; for hormone receptor-positive (Luminal) subtypes, ITPC may need to be combined with molecular/immunohistochemical analysis.